The surgical guidelines have been developed in response to a survey we completed in 2016 that identified a need for widely accessible antimicrobial guidelines for surgical prophylaxis.

National Research Council’s risk index for surgical infection:

Clean	Non-traumatic, uninfected. No break in aseptic technique, no inflammation encountered. Elective, closed primarily and no drain used
Clean-contaminated	Controlled entering of a hollow muscular viscus, minor break in aseptic technique
Contaminated	Open, fresh traumatic wound. Incision into a site with acute, non-purulent inflammation. Major break in aseptic technique.
Dirty	Pus encountered during surgery. Perforated viscus found. Traumatic wound with devitalised tissue, foreign material or faecal contamination, or of more than 4-hour duration

Guidelines

Surgical conditions	Mitigating factors	Antimicrobial recommendation	Duration of therapy
Clean		None	N/A
	Uncomplicated hernia repair75	None	N/A
	Rumenotomy76,77	Oxytetracycline	Preoperatively only
	Unsanitary conditions	Oxytetracycline	Preoperatively only78
	Periparturient79,80	Oxytetracycline	Preoperatively only78
	Surgery >1.5h	Oxytetracycline	No evidence, in other species preoperatively only
Clean-contaminated		Oxytetracycline	No evidence, in other species stop by 24h
Contaminated		Oxytetracycline	No evidence, in other species 24-48h
Dirty		Choose appropriate to infection	Choose appropriate to infection

Timing of prophylactic antimicrobials:

Tissue levels of antimicrobials are required at the time of first incision to confer protection from surgical site infection.

Intravenous antimicrobials: Administer 30-60 mins prior to surgery

Intramuscular procaine penicillin: 2h prior to surgery

Intramuscular oxytetracycline: ~8 h prior to surgery

T_max for individual drugs given by different routes can be used to assess optimal timing to achieve peak serum levels at the time of first incision.

Repeat dosing:

Dosing interval should be measured from the time of the preoperative dose. The dosing interval can be calculated as twice the elimination half-life of the antimicrobial.

Intravenous oxytetracycline: 6 hours

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